A general term used to describe midweight metallic armors worn by fighting men up until the Renaissance. Mail armors consist of small, overlapping pieces of metal but lack large, solid plates found in heavier armors.

Chainmail: armor made of interlocking metal rings.
Scale mail: medium armor made of small, overlapping metal plates, resembling the scales of a fish.

Mail is a slang sometimes said softly during anal sex by heterosexuals or homosexuals. It is said right before the penis is inserted into the other person's anus.
Note: It is never shouted or written with an "!" because during so might scare the receiever or cause them to scrim and could cause anal rupture.